In America, we have the right to "peaceably ... assemble, and to petition the government for a redress of grievances" (I want to emphasize "peaceably") as we see this young woman and many others across the nation exercising daily, and even more so (and rightfully so!) these last few weeks. The peaceful "Tank Man" was standing up to a government that did not allow that.
It is a powerful image, but not one to be compared to Tiananmen Square. Different rights, different events, different symbols.